1. Field of the Invention
The present invention relates to a magnetic tape cassette which is suitable for magnetic recording with a high density.
Nowadays, magnetic recording technology has achieved a great success and become one of the most popular recording techniques. The magnetic recording technology is mainly based upon magnetic flux differentiation and its development mainly owes to improvements in magnetic tape and magnetic head between which signals are exchanged.
Future development in the magnetic recording technology will essentially require a further increase in the recording density which in turns requires replacement of conventional oxide-type tape/head systems by metallic-type ones, and this is the reason why intense studies and developments have been achieved in the field of metallic magnetic tapes and magnetic heads for use in combination with such tapes.
Metallic magnetic tapes are broadly sorted into two types: namely, a so-called MP tape in which a dispersion of a ferromagnetic metal powder such as of iron or cobalt in a binder is applied to the surface of a polymeric film, and a so-called ME tape which is produced by forming a slant Co-Ni-O film by evaporation on a polymeric film. These two types of magnetic tapes are now widely used in 8 mm video apparatus and broadcasting instruments to cope with demands for higher recording density.
Metallic magnetic tapes also are considered to be essential for achieving high-density analog and digital recording and are expected to meet such requirements. Advances to a higher technological level are now being made through techniques for overcoming problems caused by shortening of wavelengths of recording signals, and shortcomings inherent in the tape material.
Among the problems and shortcomings mentioned above, the most critical problem to be overcome is socalled tribological problem, i.e., difficulty encountered in imparting durability to a magnetic recording layer which is finished with a high degree of smoothness in order to minimize spacing loss which becomes serious when signal wavelength is shortened. Another critical problem is that it is difficult to maintain a sufficiently large quantity of total magnetic flux and to prevent aging effects due to tape corrosion, when the tape thickness is reduced to improve the wavelength characteristic.
The following proposals (1) to (5) have been made to provide solutions to these problems.
(1) To reduce friction and wear by providing minute projections on the surface of the magnetic recording layer, as taught by, for example, IEEE TRANSACTIONS ON MAGNETICS Vol. MAG-21, No. 5, 1524-1526 (1985) and Japanese Patent Unexamined Publication Nos. 59-207422 and 61-284829. PA1 (2) To make an effective use of a partial oxidation layer without allowing the magnetic part, i.e., metallic part, to be exposed, in order to improve resistance to corrosion and wear, as taught by, for example, Japanese Patent Publication No. 57-29770 and Japanese Laid-Open Patent Publication No. 61-153856. PA1 (3) To attain a higher hardness of the material of the recording layer, thus improving resistance to wear and corrosion, as taught by, for example, Japanese Laid-Open Patent Publication Nos. 59-119532 and 61-139920. PA1 (4) To employ a protective lubrication layer so as to prevent direct contact between the magnetic recording layer and the magnetic head or the like thus giving solution to wear and corrosion without modifying the PA1 (5) To combine two or more of the proposals (1) to (4) above.
magnetic recording layer itself, i.e., by allowing the magnetic recording layer and the protective lubrication layer to play their roles individually, as taught by, for example, Japanese Laid-Open Patent Publication Nos. 60-93635, 61-131231, 61-142525, 61-151830, 61-242323, 61-250825, 61-280019 and 62-8325, and Japanese Laid-Open Patent Publication No. 61-61444.
A magnetic tape improved by the arts described hereinbefore is usually set in a tape cassette when put to use. Most of known tape cassettes are assemblies of parts molded from plastics. Considerations are given to materials, design, easiness of assembly, mechanical characteristics, weather resistances and so forth of the tape cassette in accordance with requirements of various rules and regulations. The current trend for higher recording density essentially requires that tape cassettes have sealing or hermetic natures sufficient for preventing introduction of foreign matter so as to eliminate troubles such as drop-out and clogging. Cassettes having such sealing or hermetic effects are disclosed or mentioned in Japanese Laid-Open Utility Model Publication No. 57-9983, Japanese Laid-Open Utility Model Publication No. 58-109875, Japanese Laid-Open Patent Publication No. 51-5487, Japanese Laid-Open Utility Model Publication No. 61-48481, Japanese Laid-Open Patent Publication No. 61 162290, and Japanese Laid-Open Utility Model Publication No. 61-118175.
Accordingly, an object of the present invention is to provide a tape cassette which is capable of overcoming the above-described problems of the prior art.
To this end, according to the present invention, there is provided a tape cassette comprising a trapping layer having a corrosion tendency or corrosiveness equal to or greater than that of the magnetic recording layer of a metallic magnetic tape, the trapping layer being disposed in the vicinity of the path of the tape stretched between reels on which the tape ends are wound or in gaps which provide passages for external air coming into the cassette
The trapping layer positively reacts upon selective adsorption of the corrosive gas components diffused into the cassette so as to retard deterioration of the magnetic recording layer attributable to corrosion.